The invention relates generally to power-driven conveyors and more particularly to two-material belt modules linked together to form an endless conveyor belt and methods for making those modules.
Modular plastic conveyor belts are constructed of a series of rows of thermal plastic belt modules linked together at hinge joints between consecutive rows. Hinge elements along the leading and trailing ends of each row interleave with the hinge elements of trailing and leading rows. Hinge rods interconnect the interleaved hinge elements to form the conveyor belt.
Most plastic belt modules are injection-molded out of a thermoplastic polymer forming a rigid module body that exhibits low-friction characteristics. In applications requiring a high-friction conveying surface, the low-friction thermoplastic modules are topped with a resilient material, such as a rubber compound or a thermoplastic elastomer, that provides a high-friction conveying surface. The resilient material may be mechanically fastened or molded to the hard plastic base module. U.S. Pat. No. 5,361,893, “High-Friction Plastic Conveyor Belts Having Modular Links Formed by Two Integrated Plastic Materials,” Lapeyre et al., Nov. 8, 1994, discloses a high-friction layer molded directly to the flat surface of a hard plastic module body. Molding a high-friction material directly to a flat surface works well for some thermoplastic polymers, but not for others, such as acetal. The bond between the flat bottom of an elastomeric layer and the flat, top surface of a belt module molded of acetal is not strong, and the elastomeric layer is subject to being peeled off. U.S. Pat. No. 7,222,730, “Conveyor with Nonskid Support Surface and Manufacturing Method for Same,” Garbagnati et al., May 29, 2007, discloses a skidproof covering made of a high-friction material molded onto projections on a rigid link body at a temperature higher than the softening temperature of the projection material to cause plastic deformation of the projections that originate undercuts to create a mechanical interconnection between the covering and the link body. Because the projections deform irregularly, the mechanical interconnection is not uniform and may be weaker at locations where undercuts are not deep. Furthermore, because the projections, when softened, spread horizontally to create the undercuts, they are not so useful for small-pitch belt modules that do not have much area to accommodate the horizontal spread.